1. Field of the Invention
This invention relates generally to the processing of an information signal for eliminating time base errors therefrom, and more particularly is directed to improve color video signal recording and/or reproducing apparatus in which the reproduced video signal is processed so as to cancel or eliminate time base errors contained in the chrominance component of the reproduced color video signal.
2. Description of the Prior Art
A well known apparatus for magnetically recording and/or reproducing video signals includes a rotary guide drum provided with two alternately operative transducers or heads. A magnetic tape is wrapped helically about a portion of the periphery of the guide drum and is moved longitudinally while the heads are rotated, thus causing the heads alternately to scan respective parallel tracks extending obliquely on the tape for recording or reproducing signals in such tracks.
When recording color video signals which include luminance and chrominance components, it is known to separate such components and then to frequency modulate a relatively high frequency carrier with the luminance component, while the chrominance component is down-converted or frequency converted so as to have its frequency band shifted below the frequency band of the frequency modulated luminance component, whereupon the frequency modulated luminance component and the frequency converted chrominance component are combined to provide a composite video signal which is recorded in the successive parallel oblique tracks on the magnetic tape. Upon reproducing, the composite video signal reproduced from each track is separated into its luminance and chrominance components, and the frequency modulated luminance component is demodulated, while the frequency converted chrominance component is reconverted to the original frequency band, whereupon the frequency demodulated luminance component and the frequency reconverted chrominance component are recombined to provide a reproduced standard television signal.
In the above described existing apparatus for recording and reproducing color video signals, the reproduced video signals usually contain time base errors, so-called jitter, due to mechanical vibrations generated in the tape transport mechanism and fluctuations in the rotation of the rotary transducers or heads. Such time base errors have a particularly serious effect on the chrominance component, whereby the hue of the reproduced color television picture is greatly disturbed.
In order to eliminate or cancel time base errors from the reproduced chrominance component, it has been proposed, for example, as disclosed in detail in U.S. Pat. No. 3,803,347, to provide a so-called automatic frequency control circuit (AFC) in association with the circuit for producing the frequency converting signal by which the reproduced chrominance component is reconverted to the original frequency band. In such automatic frequency control circuit, a variable frequency or voltage controlled oscillator (VCO) included in the circuit for producing the frequency converting signal has its output supplied to a frequency divider so as to provide an output frequency nominally equal to the standard horizontal or line frequency of the video signal, and a comparator compares the output of the frequency divider with horizontal synchronizing signals separated from the demodulated luminance component so as to provide a resulting comparator output voltage for controlling the frequency of the output from the voltage controlled oscillator. Although the foregoing arrangement has as its object to eliminate time base errors from the reconverted chrominance component, the compensation for such time base errors is only effected on the basis of the horizontal or line synchronizing signals included in the reproduced luminance component and, therefore, no provision is made to compensate for, or eliminate those relatively small time base errors ocurring in the intervals between the successive horizontal or line synchronizing signals.
It has also been proposed, for example, as disclosed in detail in U.S. Pat. No. 2,921,976, to compensate for or eliminate time base errors from the reproduced chrominance component by means of a so-called automatic phase control circuit (APC). In such automatic phase control circuit, the burst signal is extracted from the reconverted chrominance component and compared, in a phase comparator, with the output of a fixed frequency oscillator having the standard color subcarrier frequency. The resulting comparator output is employed to control a variable frequency oscillator of the circuit for generating the frequency converting signal by which the reproduced chrominance component is reconverted to the standard or original frequency band therefor in a frequency converter or modulator. The aforesaid automatic phase control circuit has a predetermined lock-in range and, therefore, when a sudden change, such as, a so-called skew jitter, is introduced in the reproduced color video signal, the resulting large and abrupt time base error is beyond the lock-in range of the APC circuit and cannot be immediately compensated for or eliminated by the APC circuit.
In view of the foregoing, it has been proposed, for example, as disclosed in detail in U.S. Pat. No. 3,723,638, to provide a color video signal recording and reproducing apparatus in which, during reproducing, an automatic frequency and phase control circuit (AFPC) seeks to control the frequency converting signal by which the reproduced chrominance component is reconverted to the standard color subcarrier frequency so as to eliminate or remove time base errors from the reproduced chrominance component. In such AFPC circuit the burst is extracted from the frequency reconverted chrominance component and compared with the output of a fixed frequency oscillator to provide a first control signal, and the horizontal synchronizing signals are separated from the demodulated luminance component to provide a second control signal, and the first and second control signals are simultaneously employed at least during every horizontal interval for controlling the phase and frequency of the frequency converting signal. However, at times, the first and second control signals respectively responsive to the phase of the color burst signals and the frequency of the horizontal synchronizing signals may seek to achieve contrary changes in the frequency converting signal with the result that the time base error is not completely cancelled or eliminated.